Gas indicator apparatus



No 17, 19423 @@Hfam GAS INDCTOR APPARATUS j INVENTOR.

TTQRNEYS GAS INDICATOR APPARATUS Filed NOV. 2, 1939 4 SheeiS-Sheet. 2

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ATTORNEYS 4 Sheets-Sheet 4 IN VENTOR. f .QQ-W

ATTORNEYS F. J. SCHIRM GAS INDICATOR APPARATUS Filed Nov. 2, 1939 Nov. 17, 1942.

BY M

Patented Nov. 17, 1942 UNITED sTATEs- PATENT 'OFFICE .GAS INDICATOR APPARATUS lederlck .I. Schirm,.Hoboken, N. J., assignor io Davia Emergency Equipment Company, .Incorporated, New York, N Y., a corporation o! New.

York

Application November 2', 1939, Serial No. 302,480

1 Claim.

This invention relates to gas-indicator apparatus adapted to announce at a central station the existence o1' an abnormal gas condition at one of or at any number of a plurality of outlying stations.

Although the invention is adapted forl use in 'various instances where it is essential in the interest of the preservation of life and property that a prompt and reliable indication be given as to the existence of an abnormal gas condition at one or at any number of a plurality of stations, the invention is herein illustrated as embeing` disposed rearwardly of. and adjacent'to suitable windows 2l and `22 formed in the panel. Y As shown most clearly in Fig. 2, the cabinet l houses aV valve unit 24, a suction pump 25, an

electric motor M and a suitable combustion chamber. unit 26 such as` that shown, described and claimed in United States `2,231,166, granted to Elmer L. Knoedler, Jr.,

bodied in an apparatus which is especially deis to so improve apparatus of the character to which the invention relates as to justify the placing of' complete confidence in theindications afiorded by such apparatus regarding gas conditions at the respective outlying stations.

Other objects and advantages of the invention will become apparent from the following description when taken in connection with the accompanying drawings, in which- Fig. 1 is a front elevation of an apparatus embodying the presentI invention; Y

Fig. 2,15 a lrear view of the apparatusshowing various parts thereof in elevation Fig. 3 is a plan view of a rotary valve unit;

Fig. 4 is a sectional view taken on line 4-4 of Fig. 3;

Fig. 5 is a sectional view taken on line 5-5 oi' Fig. 4;

Fig. 6 is-a bottom view of the rotary valve unit;

Fig. 'l is an enlarged fragmental sectional view taken on line 'l--l of Fig. 4, and

Fig. l8 is a diagrammatic view showing the various circuits of the apparatus.

For the sake of convenience the various units and instrumentaiities entering into the apparatus are for the most part housed within a suitable cabinet I0, the front wall oi' which serves as an instrument panel P with which are associated a control switch Il, a relay meter I2. a jack unit I4 (which includes a pair of normally closed switches lla and Hb diagrammatically shown in Fig. 8), an index unit I5, a plurality of signal lamps Il, Il, I8, andan annuneiator unit 20,

February 11, v194.1. The pump is of conventional design having a pair of rotors (not shown) whichv are operatively connected together by ay pair of gears 21 and are driven by the motor M. With the pump 25 there is associated a gearreduction unit 28 which-includes a worm 30 suitably connected to one of the pump rotors and meshing with a worm gear 3|, with which is associated a worm 32 meshing with a worm gear 34 carried by a vertically disposed shaft 35, which is driven at a relatively slow speed and to the upper end of which is connected an arm 31 having at one end a yertically disposed cam pin 38 adapted toy eil'ect step-by-step rotation of 'a slotted cam plate 40 associated with the valve unit 24 and serving] in conjunction with its coinafter more clearly appear.

. by whicha series of tube-like inletlconduits Ib,

the index unit I5 andthe annunciator unit 2U 55 operatively related cam pin; as a Geneva movement b'y' which is attained the desired operation of the valve-unit 24.

The valve unit 24 comprises, particular reference being had to Fig. 4, a frame-like structure 4I which includes an annular or sleeve-like body 42, from which extend downwardly and inwardly a plurality of arms 44, by the lower ends of which are carried a hub-like web provided with a suitable bearing 4B, within which is journalled a shaft 41 to which'the slotted cam platey 40 is connected and t0 which there is also connecteda bevelled gear 48, lthe function o1' which will hereinafter more clearly appear. The sleevelike'body 42 is providedinteriorly thereof with an annular shoulder adapted to receive thereon a hard-rubber port plate 5I, which is adapted to be screwed' into the sleeve-like body 42 and there held againstdisplacement on the annular shoulder 50.- The plate 5I is provided with an outlet port 52 and `a plurality of inlet ports la, 2a, 3a, 4a, 5a and 6a. The ports liz- 6a inclusive are disposed in an. annular group about'the port 52 and are adapted to be progressively placed in communication therewith incident to intermittent operation of the valveunit 24, aswill here- The port -plate 5| is provided with a plurality of pipe couplings 54 2b, 3b, 4b, `5b andBbl are connected to the port plate 5I and maintained in communication with Patent No.

the respective inlet ports ica-8a inclusive. The

pipe coupling 55, which communicates with the outlet port 52 and by which a tube-like delivery conduit 51 is connected to the port plate and maintained in communication with the outlet port 52. The tube-like conduit 51 is in turn connected to the gas inlet port (not shown) of the combustion chamber unit 25, which, as will be readily understood, is connected by a suitable tube-like conduit (not shown) to the inlet port (not shown) of the suction pump 25, so that under certain conditions, Yhereinafter more particularly described, gas is drawn under the action of the suction pump through the conduit 51 and the combustion chamber unit 25, such gas being discharged from the pump by way of its exhaust port 58. l

In order that the conduits I b--Bb may be suc'- cessively placed in communication with the combustion chamber unit 25 by way of the conduit l, there is associated with the port plate 5i a hard-rubber valve plate 50, a ripheral bearing for which is aiorded 'oy the sleeve-like body 42 oi the frame-like structure `ii, as shown mostclearly in Fig. fi. The upper face of the valve plate @il intimately engages the lower face of the port plate 5i and is provided with a radially extended grcove-like channel 5i, which is mairi-j tained at all 'times in communication with the outlet port 52 and is adapted to establish communication between that port and the respective inlet ports itt-ic as the valve plate intermit tently rotated under the action of the shaft 41 to which the valve plate is connected. As shown roostl clearly in Fig. 4, the driving connection afforded between the shaft t1 and the valve plate GS comprises an anchor ange 52 secured to the valve plate Se by any suitable means such as a bolt 54. Preferably the shaft 41 extends upwardly beyond the flange 52 and is there accommodated within a central recess or pocket 55 formed in the lower face of the valve plate 50. In order that the valve plate 6U may be maintained in intimate face-to-face engagement with the adjacent port plate 5I, a thrust spring 55 is employed. This thrust spring 55 at its upper end the valve plate 60. The lower endA of the spring 55 snugly fits within a cup-like retainer 51, which is loosely supported on the bearing I5 and Y through which the shaft l1 loosely passes. The anchor flange 52 and the cup-like retainer 51 eifectively serve to maintain the thrust spring 5B coaxially disposed with respect to the shaft 41 and the valve plate 50, which shaft is free to move upwardly, due to the slight clearance aiorded between the bearing l5 and the hub-like portion of the slotted cam plate 40, under the action of the thrust; spring 56 incident to the occurrence of any gradual upwardwear-compensating displacement of the valve plate 60 under the action vof the thrust spring.

surrounds the anchor flange 62 and there engages 'scavenging ports 68 that each such group is so located with reference'to the next succeeding one of the inlet ports Ia--Ba and the immediately preceding one of such ports that the combustion chamber unit is opened to the atmosphere pursuant to the completion of the examination of the atmospheric condition at one outlying station and immediately prior to such time as the examination of the atmospheric condition at the next succeeding outlying station is initiated. By way of further explanation in this connection, let it be assumed that the valve plate 5U is so moved in a clockwise direction, reference being had to Fig. 3, as to sever communication between the inlet port 4a and the outlet port 52 of the valve unit` 24. Under the conditions just assumed, it will be understood that incident to severing communication between the inlet port la and the outlet port 52, the gaseous content oi the combustion chamber unit 25 is representative of the atmospheric condition prevailing at the outlying station corresponding to the inlet port a at the time or making the last examination. Prior, however, to such time as communication is established between the outlet port 52 and the next succeeding inlet port 5a in order that an 'examination may be made of the atmospheric condition at the outlying station corresponding to that inlet port, the outlet port is placed in communication with that group of scavenging ports 68 which immediately precedes the inlet port 5a, with the result that the gaseous contents of the combustion chamber unit and its associated'con duit 51 are supplanted by air admitted by way of the group of scavenging ports just mentioned and known to be pure in character. By supplying the combustion chamber unit 25 and its associated conduit 51 with pure air immediately prior to initiating an examination of the atmosphericcondition at the respective outlying stations, the examination of the atmospheric condition at any given outlying station cannot be influenced by the atmospheric condition prevaling at the immediately preceding outlying station at the time the examination was carried out with respect to such preceding station.

In order that certain electrical circuits, hereinafter more particularly described and corresponding to the several outlying stations, may be closed under conditions and for the purpose hereinafter more particularly stated, the port plate 5I and valve plate lll of the valve unit 24 are utilized respectively as the stationary element and rotatable element of a multiple switch 10 which is diagrammatically shown in Fig. 8. This switch includes a plurality of stationary contacts Ic, 2c, 3c, 4c, 5c and Bc which by means of binding posts 1l areconnected to a return conductor 12 leading to a battery B, the contacts being carried by the port plate 5I and having their contact faces flush with the lower surface of that plate. Associated with the contacts' lc-Ic are a plurality of similar contacts Id, 2d, 3d, 4d, 5d and 5d which are equipped with binding posts 12 adapted to accommodate the terminals of various conductors hereinafter more particularlyv described. In order that the respective pairs -of contacts Ic, Id-Sc, 8d may be bridged or closed successively incident to rotation of theA valvey plate 60, such'plate is provided with a bridge unit 18 which includes a pair of plunger-like contacts 14 and 15 accommodated within pocket-like recesses 18 formed in the ivalve plate. These contacts 14 and 15 are normally urged upwardly under the action" of apair of compression springs 11, the upperends of which engage the headlike'portions of the contacts and the lower ends of which rest on the bottom wall of the pocketlike recesses through which extend for sliding movement the stem portions 18 and 80 of the respective contacts, the stem portionsbeing connected together Aat their Alower ends by a conductor plate 8|. Concerning the disposition of the respective pairs of contacts Ic, Idf-Ic, 5d

with relation to the inlet ports Ia-4a, it will be noted that, during such time'as the valve plate 50 is stationary and communication is maintained between the outlet 'port 52 and one of the inlet ports, the particular pair of contacts which corresponds to the inlet port then communicating Referring to Figs. 1 and 2, the index unit I5 includes a rotary indicator dial 88 provided at its louter margin with a series of numerals, which correspond to the respective outlying stations and are successively presented to view by way of the window 2| formed in the instrument panel P. The indicator dial 88 is carried by a horizontally disposed shaft 90, suitably supported within the cabinet I and provided at one end with a bevel gear 9| meshing with the bevel gear 48secured tothe lower end of the shaft 41 to which the rotary valve plate 60 is connected for step-bystep rotation under the action of the cam plate 40. Inasmuch as the index unit I operates in synchrony with the valve unit 24, one may readily determine at any time the position of the rotary valve plate 60 with relation to any one of the several outlying stations towhich lead the tube-like conduits Ib-Bb, it being understood that during s 'uch time as an examination of atmospheric conditions at any one of the several outlyingstations is being carried out, the numeral carried by the indicator dial 88 and corresponding to such one station will be maintained in view by way of the window 2|.

The annunciator unit is herein illustrated as `being of the so-called drop type, and is characterized by the fact that i't includes a plurality of indicator tabs 92 which are pivotally supported for individual movement under the action lof gravity from their respective retracted positions to their respective announcing positions. The indicator tabs 92 are provided with numerals core 1 responding to the respective outlying stations to which lead the conduits IIJ-6b, the numeral of any one of the several indicator tabs being pre- 4 sented to full view by way of the window 22 as shown inl Fig. 1. The maximum swing of the Y needlel in a clockwise direction is determined by a stop pin\85, a similar stop pin 85 being employed to limit the movement of the needle in a counter-clockwise direction. 'These stop pins are adapted to be moved, under certain conditions hereinafter more particularly described, toward each other by a reset solenoid RS (Fig. 8) so as to overcome the holding effect of the magnet 82 on the indicator needle 84 as it is brought to a centra] position with reference to an appropriately'graduated indicator scale 86 with which the relay meter I2 is provided. The relay meter I2 is further characterized by the fact that its indicator needle 84 serves as a switch element S-I,

which is associatedwith aconventional needleactuating armature 83, or its equivalent, and is adapted when moved to its extreme position shown in Fig. 1 to engage a second switch eleindicator needle 84 serving as a switch element S-I, the needle-actuating armature 83, the stop pin 8%,v the stop pin 85', the reset solenoid RS, the switch element S-2, and the operating magnet 81.

such tab assumes its announcing position. Normally the indicator tabs 92 are maintained in their respective retracted positions by pivotally supported latches -94diagrammatically shown in Fig. 8. These latches constitute armatures for a series of release magnets Ie--Ee and are adapted to be moved under the influence of such magnets in a counter-clockwise direction from their norelectrical circuit oi the Wheatstone bridge type is vemployedvthe circuit being characterized, as is well known. by the fact that it may be employed/ to indicate a change of electrical resistance in one of its parts.

In Fig. 8; a circuit of the above type is-illustrated in the present embodiment of the invention as including resistances R1, R2, Fs'and F4, the resistances F3 and F4 being in the Vform of, and sometimes hereinafter referred toas, laments. lThe resistances R1-R2, R1-F3, R2-F4, and Fae- F4 are respectively connected together by conductors 96, 91, 98 and |00, the conductors 96 and 98 beingv connectedto the battery B by way of conductors |02 and |04 in the latter of which the control switch Il is disposed. Also in the conductor |04 there is disposed the operating winding |05 of 'a bridge relay |06, inparallel with which Winding it has been found desirable to place a fixed resistance 101, the Value of which may be determined by taking into account the electrical characteristics of the operating winding with which it is associated. The bridge relay 06 also includes a pair of movable contacts i08 and HG which are electrically connected to the conductor 04 and are adapted to be moved simultaneously incident to energization oi the operating winding IUS. Movement of the contacts ISS and iid upon energization of the operating winding 55 causes the former of these contacts to engage its associated switch terminal i ii and the latter of these contacts to disengage its associated switch terminal l l2. At the instant the contact iBS engages its associated switch terminal ii i, a circuit is established through the motor M from one side of the battery B to the other side thereof by way of the conductor |04, the contact MJS, the terminal i i i, a conductor i I3 leading to the motor, a conductor H3 leading from the motor and the return conductor 'l2 to which the conductor H3 is connected. At the instant the circuit ci the motor M is established the lamp il, which is preferably colored to eiect green illumination, is oi course energized, since it is connected across the motor circuit by way oi conductors il" and ii". The motor M and lamp il. remain energized so long as the switch remains closed and so long as the bridge relay is maintained energized, `However, in the event either the filament F3 or the iament Fi burns out while the switch ii reina 'is ciosed, the circuits oi the motor li lamp are opened and the circuit of the iarnp it, which is colored to effect amber illumination, is closed by Way of the conductor i, contact W* terminal H2, conductor i3 and co; ductor in this connection it is to obse of the filaments F3 sistance then ceci conductor idf-3 vent the iow or" s circuit to inaintai circuit condition and the lamp from an inspect ing or" the dent to closing t established being c i battery ifii to the cti Ff. burn out, the reto the circuit in which is included such as to Tore- `cient current through that t-.e bridge relay W6 in closedth relation to the motor M .clis will be readily understood i Jig. the operating winday lG is energized inciitch ii, the circuit thus from one side of the ier side thereof by way of the conductor ie resistances Rif-Rz, Fs-Fi and the conductor The bridge circuit also includes the magnet 'winding 8l' of the operating magnet reference being had to 'the switch S, which winding is connected, on the one hand, to the conductor by a conductor H4 (Within which is disposed the jaci. switch ila) and, on the other hand, to the conductor i by way of a conductor .@5, Within which is disposed the iacli switch iiib. in order that the bridge circuit may be balanced as occasion may require to compensate, for example, Yfor any graduai change in the characteristics o the filaments F3 and'i, there is interposed in the conductor it@ a resistance Re which, in conjunction with a wiper arm HS interposed in the conductor iid, constitutes a potentiometer Pi. is to the potentiometer PI,

it will be understood that by moving its wiperl arms H5 in one direction or the other, `as required, along the resistance R5 the bridge circuit, assuming the switch H to be in closed-circuit position and that stable ambient conditions prevail in the immediate vicinity of the filaments F3 and may be brought into a perfectly ballanced condition, which condition is indicated when the indicator needle 8l of the relay meter I2 assumes a designated position, for example, zero-position, on the meter scale 86.

The filaments F3 and F4 are housed within suitable vchambers (not shown) of thecombustion chamber unit 26 in accordance with the disclosure of the above-mentioned patent application, the chamber carrying, for example, the lament F3 being sealed to the atmosphere so as to maintain that filament under stable ambient conditions and the chamber within which the filament F4 is housed being connected to the pump 25 and the conduit 51 so as to enable that lament to be subjected to gases derived from -the several outlying stations for individual examinations.

In order that a stable ambient condition may be insured with respect to the filament F4 when balancing the bridge circuit through the instrumentality of the potentiometer PI, the conduit 51 is provided at a point intermediate the valve unit 24 and the combustion chamber unit 2B with a conventional type of three-way valve Va. The valve V3 is normally maintained (as by a spring, not shown) in such position that communication is afforded between the valve unit 24 and the combustion chamber unit 2G, the valve being equipped with a lever or handle, as shown, by which it may be manually moved to and held in such position that the combustion chamber unit is closed with respect to the valve unit and opened to the atmosphere by way of a suitable inlet port, not shown, with which the valve is provided. The spring just 'mentioned as associated with the valve V3 is adapted to move that valve to its normal position and is, therefore, adapted to so function as to insure the closing of communication between the combustion chambeim unit 2E and the atmosphere in the immediate vicinity of the apparatus and the establishing of communication between that unit and the valve unit 24 pursuant to the carrying out of a balancing adjustment of the bridge circuit.

From the foregoing description of the Wheatstone bridge circuit and its relation to the combustion chamber 26, it will be understood that any burning of gas in the immediate vicinity of the filament F4 will augment the normal heat inherent in that filament so that the filament resistance is increased with respect to the unaffected resistance of the filament F3. Such lncrease in filament resistance will electrically unbalance the Wheatstone bridge circuit with the result that current is caused to flow across the bridge circuit by way of the magnet winding B1', thus energizing the magnet 81 which causes the indicator needle 84 to move in a clockwise direction (reference being had to Fig. l) or in a counterclockwise direction (reference being had to Fig. 8). The various electrical factors entering into the circuit arrangement peculiar to the present invention may be such that a closedcircuit relationship between the indicator needle t4 (switch member .S-I) and its associated switch member S-2 is effected at a predetermined point well below (say, at one third) the lower explosive limit of some given gaseous mixture such, for example, as gasoline vapor and air, in order that a warning signal or alarm :nay be given in the manner hereinafter more particularly described while there is still time to investigate and correct the cause of the dangerous condition.

Incident to establishing a closed-circuit con- 2,302,061 dition between the indicator needle 84 (switch tact |08, the terminal a portion of the con-'- i ductor ||3a portion ofthe conductor I1', a conductor I1 (within which the operating winding ||8 of the relay magnet |20 is disposed) the switch member S-|, the switch membenS-Z and its associated conductor |2|, the conductor |02 `and a portion of the conductor 12. The annunciator relay unit AR includes a pair of movable contacts |22 and |24, which are, electrically connected to the conductor ||1 and are adapted to be moved simultaneously incident to energiaation of the operating winding ||8, the circuit of which includes the conductor |11 leading to the switch member S--I of the switch S forming a part of the relay meter |2. Movement of the contacts |22 and |24 upon energization of the operating winding ||8 causes these contacts tol engage their respectively associated switch terminals |25 and |26, the terminal |25 being`connected to the conductor 95 which is common to the branch conductors |f-6f included in the individual circuits of the respective release magnets Ie--6e of the annunciator unit 20 and the terminal |26 being connected to the return conductor 12 by way of a conductor |21 within whichis disposed the operating winding |28 of 'the reset solenoid RS, the function of which is to automatically open the switch S of the relay meter |2 by moving the stop pins 85 and 85" toward each other, as previously described, so as to overcome the holding effect of the magnet 82 (Fig. 1) on the indicator needle 84 and bring that needle to va central position with reference to the indicator Vscale 86 with which the relay meter is provided. It will be understood, of course, that it becomesnecessary to break the holding effect of the magnet 82 on the needle 84 after the switch Sv has assumed closed circuit position, because otherwise that switch would be permanently held in closed circuit position which means that the annunciator relayVAR would/be constantly energized with the result that the several release magnets |e6e would be operated .insuccession regardless of the atmospheric condition atv their corresponding outlying stations. AsA to thefstop pins 85 and 85'-, it is to be noted that since they are moved toward each other as the needle 84 is forcibly moved out of closed circuit position any tendency of the needle to unduly oscillate or swing from one position to another incident to its release is quickly and eiectively over-come.. At the instant the contact |22 |25,'an annunciator circuit is established from one side of. the battery B to the other side thereof by way of contacts |08 and ofl the bridge relay |06, portions of conductors `||3`and i1', the conductor ||1, the contact |22 and the terminal |25 of the annunciator relay AR, the conductor v96, one of the branch conductors |f6f, one of the contacts |d-6d, the bridge unit 13, one of the contacts |c-6c and the return conductor 12. In considering .the several annunciator circuits, 'which respectively include the branch conductors |f4-6f, it is to be observed that the particular annunciator circuit which is es,- tablished by way of the conductor 95, incident to the closing of the switch S with which the engages its associated switch terminal -operate as to unlatch such annunciator tab 92 ascorresponds to the outlying station at which the atmospheric condition is responsible for the establishment of a closed-circuit condition oi the switch S.y Immediately pursuant to the unlatch- `ing of an annunciator tab 92, the reset solenoid RS operates to open the switch S, whereupon the operating winding ||8 of the annunciator relay unitAR is deenergized incident to which the circuit of the operating winding |28 of the reset solenoidgRS is deenergized, thus allowing the stop pins 85 and 85' to returnto their normal positions shown in Fig. 1. y Should the indicator needle 84 (switch member S|) move again to its closed-circuit position with relation to the switch member S-2 prior to such time as communication between the combustion chamber unit 26 and the outlying station at which the atmospheric 'condition was responsible for the establishment of a closed-circuit condition of' the switch S in the rst instance, the annunciator relay unit AR and the reset solenoid unit RS are again operated in the manner just described but the consequential energization and deenex gization of the previously established annunicato.

circuit does not, of course, in any way affect` the-already lreleased Yannunciator tab 92 unless such tab has been moved during the interim to its retracted or latched position. Here it is to ber observed that any suitably manuallyoperkated means, vsuch as a reset button |3|, may be employed for moving the annunciator tabs 92 to their -retracted or latched positions, such button being common to all of such tabs as is well understood in connection with conventional mechanical resetting mechanisms .in the annunciator art.

other side of the battery by way of the conductor |04, the contact |08, the terminal a, portion of conductors 3 and I1', conductor H1, contact |22 and its associated terminal |25. Incident to energization of the latch relay magnet |34,-its

` associated switch |36 is moved to closed-circuit the switch member |4| .in closed-circuit condition relay meter l2 is equipped, corresponds to the 75 position, thereby establishing a circuit through A' the lamp |6, which is colored to eect red illumination, Abyway of conductors |38 and |40, connectedrespectively, to the conductors. ||1 and 12.w Incident to establishing the lamp circuit, the switch member |4| of the switch |36 is locked in closed-circuit position by any suitable latching mechanism which, as will be readily understood by those skilled in the art, is adapted to maintain until such latching mechanism is manually released. It will be obvious to those skilled in the art that the releasing operation of such latching outlying station with respect to which an exam- 4 mechanism as may be employed in connection with the switch member 14| may be conveniently effected through the medium of the reset button i3! already described as adaptedfor use in effecting manual return of the annunciator tabs 82 to their retracted positions. s

From the foregoing description or the apparatus embodying the present invention, it becomes apparent that whenever a mixture of a combustible gas is encountered at oneof the outlying stations to which lead the several conduits lli-6b, a closed-circuit `condition of the switch S is eiected, provided, of course, the volume of combustible gas with respect to the volume of air commingled with such gas is such that the filament Fi is so heated incident to the burning of the combustible gas within the combustible chamber 26 that the filament resistance is increased to such an extent that current of suilicient value is caused to flow across the bridge circuit to effect movement of the switch member S-I into engagement with the switch member S 2. In this connection, it is to be borne in mind, as previously explained, that a closed-circuit relationship between the switch members S--I and S2 is eiiected at a predetermined point well below' (say at one-third) the lower explosive limit of some given gaseous mixture such, for example, as gasoline vapor and air. Whenever a dangerous atmospheric condition point, with respect to the lower explosive limit,

at which the switch S is closed) is encountered at an outlying station, the annunciator 2li operates to announce the outlying station at which the dangerous atmospheric condition is encountered; and substantially simultaneously with such an announcement the lamp i6, which is colored to eiect red illumination, is energized so as to give further warning to the effect that a dangeious atmospheric condition has been encountered. At all times during normal operation of the apparatus the circuit of the lamp il, which is colored to effect green illumination, is maintained closedbut should the Wheatstone bridge circuit be rendered inoperative by reason of the burning out of either the filament Fs or the iilament F4, the operating winding of the bridge relay IUS is so deenergized, as previously explained, that the circuit of the lamp i1 is automatically opened and the circuit of the lamp I8, which is colored to eiect amber illumination, is automatically closed so as to indicate the burned out condition of one or the other of the illaments. In view of the fact that the switch S of the relay meter i2 is closed, as previously explained, at a point well below (say, at one-third) the lower explosive limit of some given gaseous mixture such, for example as gasoline vapor land air, and

in view of the fact that the indicator needle B4 (switch -member S|) of such switch is incapable of movement beyond its closed-circuit position, it has been'deemed advisable to provide means to enable one to readily determine the exact character, -from an explosive standpoint, of the gaseous mixture encountered where such mixture is at least suiiiciently rich in combustible gas to cause the switch S to assume a closed-circuit condition, and to this end the jack unit ll is employed to enable a galvanometer G to be easily and quickly connected across the Wheatstone bridge circuit where it temporarily supplants the relay meter I2. The galvanometer G is equipped with a suitable connector such as a conventional telephone plus |42 which, when inserted'in the (as determined by the jack unit H, opens the switcAie: Ha and Hb of that unit, thereby cutting the relay meter I2 out of circuit and substituting for that meter the galvanometer which is provided with a graduated scale, not shown, adapted to function in conjunction with its associated indicator needle, not shown, to give an accurate indication of the character of the gaseous mixture from an explosive standpoint, thus enabling one to readily determine the extent to which a combustible gas is present in the encountered gaseous mixture. Although the primary function of the galvanometer Gis to enable one to determine the exact character, from an explosive standpoint, o! an encountered gaseous mixture which is such that the switch S is caused to assume a closed-circuit condition, it will be understood, of course, that the galvanometer may also be utilized to determine the exact character, from an explosive standpoint, of an encountered gaseous mixture when such mixture is insufliciently rich in combustible gas to cause the switch S to assume a closed-circuit condition. A

Although only one form of the invention is herein shown and described, it will be understood that various changes may be made without departing from the spirit of the invention or the scope of the following claim.

A divisional application, Ser. No. 403,155, nled July 19, 1941, describes and claims the means described in this application by which the control circuit is rendered incapable of functioning in response to the burning out of a filament so as to erroneously indicate the presence of a dangerous gas condition, and the means by which a signal indicative of a burned-out filament condition is set upat the instant such condition occurs, in order that the attendant of the apparatus may be prompted to remedy the burned-out filament condition and thus recondition the impaired Wheatstone. bridge circuit for normal operation without delay.

What is claimed is:

A gas indicator apparatus for use in carrying out an examination of atmospheric conditions at a plurality of outlying stations in succession, comprising a combustion chamber unit, means for effecting delivery of atmospheric samples to said combustion chamber unit from said outlying stations in succession and including a plurality of inlet conduits leading to said stations, a delivery conduit leading to said chamber, a valve unit having a plurality of scavenging ports and including a movable valve member common to said conduits and adapted to successively connect said stations with said chamber by way of said delivery conduit and said inlet conduits, valve actuating means !or advancing said valve member to successive conduit-connecting positions and operating to open said delivery conduit to the at'- FREDERICK J. SCHIRM. 

